System projections vs user defined projections

In terms of performance , is there any difference between “system projections” vs “user defined projections” i.e. what is the benefit of system projections over same created via ser defined projections

system projections are written in c# and execute without the cost of marshalling v8 calls so are slightly faster.

Thanks James. Only drawback of system projection, it would multiply write across DB for each event although slightly faster.